1. Technical Field of the Invention
The present invention relates to fabricating methods for annular component parts and, more particularly, to a method of fabricating an annular component part, playing a role as a stop collar available to be mounted on an output shaft of a starter for startup of an engine, a die for use in such a fabricating method and an annular component part fabricated by such a fabricating method.
2. Description of the Related Art
In the related art practice, as shown in FIG. 14, a starter has an output shaft 100 slidably carrying thereon a pinion 110 that is moved into meshing engagement with a ring gear (not shown) of an engine. With such a starter, attempt has heretofore been made to mount a stop collar 120 on the output shaft 100 by means of a snap ring 130 with a view to restricting a shift position of the pinion 110 as disclosed in Japanese Patent examined Publication No. 6-78746.
The stop collar 120 has been fabricated by a method in the related art practice, which will be described below with reference to FIG. 15.
The fabricating method comprises:
(1) Cutting and Forging: Bar steel is cut into process raw material in a given length and then subjected to forging to form a steel bar member 200 as shown in FIG. 1.
(2) Softening and Annealing: The forging formation results in hardening of the steel bar member 200, which is annealed and softened.
(3) Barrel Grinding: Barrel grinding is conducted to remove oxidized scale from a surface of the steel bar member 200.
(4) Lubricating Film Treatment: Bonderizing treatment is conducted to form a phosphoric acid film on the surface of the steel bar member 200.
(5) Cold Forging (Molding) Step: Cold forging extrusion forming is carried out on the steel bar member 200 to form a workpiece 202 with a cylindrical wall 202a and a bottom wall 202b having a downward protrusion 202c as shown in FIG. 15B.
(6) Cold Forging (Punching) Step: Punching is carried out to form a bore 202d on the bottom wall 202b of the workpiece to form a workpiece 202A formed with an annular flange 202e at a lower end of the cylindrical wall 202a as shown in FIG. 15C.
(7) Cutting (Undercut): An inner circumferential periphery 202f of the workpiece 202A is formed with an annular concave portion 202g in the form of an annular recess by cutting to provide a workpiece 202B as shown in FIG. 15D.
With such a fabricating method set forth above, since the workpiece is formed by cold forging work that results in an increase in deformation of a whole of the raw material, a need arises for conducting specific processes including softening and annealing, barrel grinding (for removing scale) and lubricating film treatment. Moreover, since cold forging work is hard to form a depression in an undercut shape, a separate cutting machine needs to be used for the cutting operation. As a result of these consequences, the related art practice encounters various issues with an increase in processing time and a need for preparation of processing equipment only for such cutting. Another issue includes an increase in inventory holding cost and requisite space or surface area on an intermediate production process. Additionally, a drop occurs in productivity in spite of the product's simple structure and it's difficult to shorten the delivery schedule. Moreover, due to large energy consumption, the softening and annealing step and the lubricating film treatment go against the trend of modem energy saving solution.